Published on August 29th, 2016 | by Zachary Shahan0
Tesla Battery Improvements & Tesla Model 3 — Randy Carlson Dives In
August 29th, 2016 by Zachary Shahan
Randy Carlson has developed a strong following and positive reputation among Tesla enthusiasts due to his in-depth Tesla articles on Seeking Alpha. He has been working hard to uncover unknowns about Tesla batteries, the Tesla Gigafactory, the Tesla Model 3, and so on. Basically, the aim seems to be better understanding how much of a competitive advantage Tesla has in the EV industry, whether it is on track to hit its Model 3 targets, and whether it is a safe/good investment.
Full disclosure: This is in my short bio under the article, but I figure I should highlight here right off the bat that I’m long TSLA because I think Tesla has several critical competitive advantages in the ripe-for-disruption auto industry.
People keep sending me Randy’s latest article, and I just got around to reading it, so I wanted to highlight it for others to enjoy and in order to especially highlight (and start a discussion about) some of his key assumptions and conclusions.
[Update Aug 30: Just to clarify, the statement from Tesla that the P100D battery cells don’t contain any chemistry changes doesn’t by default disprove Randy’s theory expressed below. As he wrote, “Tesla isn’t about to try increasing per-cell voltage in the big pack (96 cells in series) because that would put the pack voltage above the SuperCharger capability — and probably above the design max for inverters in the drivetrain, too. The small pack (14 modules, 84 cells in series) would be the logical place to try greater per-cell voltage.” Another commenter, “molli,” added: “There is no evidence against Randy … that is the point. The way I see it Tesla has two development goals (a) to make the low end car cost less and (b) push the performance. (a) and (b) do not have the same solution — that is what we learned. Tesla spread the risk by separating new cell chemistry into the 60/75 pack and the new cooling & BMS system into the 100 pack. Smart, very smart.” I am not claiming that Randy’s theory is correct, but I am hopefully clarifying a debate here whether or not the postulated cell changes in the smaller battery packs by default disproved Randy’s theory.]
Being more fit for a list-style piece, here’s a list of key statements and conclusions from the article:
- “To date, neither Tesla or Panasonic have publicly disclosed cell chemistry with high enough specific energy for a successful Model 3.”
- However, batteries in the Tesla Model S and Model X have improved considerably in the past year, seemingly from improvements in chemistry.
- Although Tesla Tap concludes that the 60kWh Tesla battery contains 5,040 cells and the 70/75kWh pack 5,880 cells, Randy argues that doesn’t make sense since major auto media outlets published curb weights for the Model S 70D and Model S 60D that were essentially equal. If there were 840 more cells in the Model S 70D, it would weigh a lot more than the 60D (approximately 85 lbs or 39 kg more). [Update: And, by the way, Tesla has stated that the Model S 60 has the same battery as the Model S 75, but is just software limited.]
- “But, how can Tesla get 75kWh into the same cells that, in the initial design, would hold only 60kWh? Well, there are two ways. Improved cell chemistry can allow more Ahr (Ampere-hours) of charge at the same voltage per cell. Or, improved cell chemistry can allow each cell to be charged to a higher voltage, cramming more charge into each cell. The US Department of Energy and other researchers have been working hard on both of these approaches and surely Panasonic has, too. Since both approaches can be combined, some degree of higher Ahr capacity and some increase in per cell Voltage are likely to be seen in improved Tesla/Panasonic cells.”
- Skipping some details on Supercharging and jumping to Randy’s next conclusion (based on those details): “Tesla’s small battery configuration can take advantage of cell capacity increases resulting from higher voltage cells, but the large battery configuration cannot. This difference in ability to achieve higher per-cell voltage between Tesla’s small and large batteries conveniently explains why the 85kWh large battery was increased by only 5.9% (to 90kWh) while the 60kWh small battery gained 25% more capacity (to 75kWh). If the cells used by Tesla today have ~6% greater Ahr capacity at 4.2 Volts and can be charged to slightly higher per-cell voltage to achieve another ~18%, the difference between the large capacity gain of the small battery and the smaller capacity increase of the large battery is explained.” [Note that this statement came before the release of the P100D.]
- Randy is convinced Tesla achieved this through a higher-voltage electrolyte, and that changes have potentially also been made to the anode and cathode.
- Making the same essential change in battery chemistry for a Model S with a larger battery pack results in a 100 kWh battery, which is what Tesla just unveiled. This can also explain the quicker acceleration — 0–60 mph in just 2.5 seconds.
- “Changing to a high voltage electrolyte has negligible effect on the weight of a lithium cell, but as described above, operating cells at higher per-cell voltage substantially increases the amount of energy that can be stored.”
- “Analysis of recently introduced Model S/X battery configurations shows Tesla/Panasonic are already making and selling batteries with improved cell chemistry. The coming P100D is likely to use cell chemistry with specific energy high enough to cross the ICE-to-BEV disruption threshold (385 Wh/kg); chemistry good enough to make Model 3 cars that best the BMW 3 Series on weight, performance and cost.” [Again, note that this statement came before the release of the P100D.]
- “With cell chemistry in today’s 75kWh Tesla battery, the long range Model 3 version will have 250+ miles of EPA range. Cell chemistry expected in the P100D will give nearly 300 miles. And, the Model 3 battery configuration allows further chemistry advances to push range higher still.” [Note that the EPA-rated range of the new Model S P100D is expected to be ~317 miles, quite a bit higher than Randy projected.]
I’m not a battery scientist, but this string of thoughts and research seemed interesting enough to get a discussion going here on CleanTechnica among genuine battery experts, as well as more armchair-variety battery enthusiasts. Are Randy’s ideas here spot on? Deeply flawed? Baked in chocolate and covered in delicious electrolyte-heavy icing?
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